On the horizon

ByPeter N. SpottsApril 27, 2006

Excessively warm water can bleach and kill coral - a key concern marine scientists have about global warming. Coral reefs are nurseries for ocean life.

Now, a trio of scientists has uncovered a mechanism that allows some corals to survive bleaching events. In essence, some bleached corals bounce back by dining on zooplankton that float by. This gives these corals emergency rations in the absence of algae that normally grow on them, give them their color, and provide nutrients. The results offer hope that coral reefs may be more resilient than previously thought - with coral species that exhibit the most varied diets likely to anchor reef recovery and emerge as the dominant species.

A team led by Ohio State University marine scientist Andrea Grottoli put several types of coral into tanks of sea-water and heated the water to coral-bleaching levels. They found that one species of branchlike coral, Montipora capitata, survived and recovered. The difference, researchers say, was that Montipora could take in food on its own, without the aid of the algae that high temperatures killed. The results appear in Thursday's issue of the journal Nature.

Some 34 million years go, Antarctica had virtually finished its shift from a continent covered with forests to a continent covered with ice. That shift may have been triggered by Antarctica's break from what today is South America, researchers now say.

Some suggest the Big Chill began when South America parted company with Antarctica. A gap already had developed between Antarctica and Australia. The new gap let ocean currents circulate nonstop around the southern ocean. The circulation kept warmer, subtropical waters from reaching Antarctica.

A team from the University of Florida drilled into the sea floor deep beneath the South Atlantic, pulled up sediments bearing fossilized fish teeth, then analyzed the tooth chemistry. They found the Pacific's geochemical imprint in the teeth, which they estimate are 40 million years old. Their conclusion: Circumpolar current appears to have emerged during the same period that Antarctica was building its icy mantle, and may even have caused the change. The results appear in the current issue of the journal Science.

Silent star killers

Old supermassive black holes in galactic centers may look quiet; but looks can deceive. A team of astronomers has found that these enormous black holes are far more active than they appear, to the point of extinguishing star formation in regions of the galaxies they inhabit.

Black holes are objects with gravity so strong that even light cannot escape. They come in a variety of sizes, including supersized black holes found in galaxy centers. So far, astronomers have focused largely on galaxies with active central black holes, which trigger bursts of radiation from material heating and colliding as it falls into the black hole.

But an international team of astronomers has been interested in the black holes that don't "bark." Radiation from the regions around these black holes seemed too low, given the amount of material falling into them. Using data from the Chandra X-ray Observatory, the team found that in addition to radiation, the geezers generate high-energy particles. This outflow can clear interstellar gas out of vast reaches of space, generating bubbles deprived of the stuff from which stars form. The results are due to appear in an upcoming issue of the Monthly Notices of the Royal Astronomical Society in Britain.